Captain 'conducted unusual procedure'

The captain of the AirAsia flight that crashed into the sea in December left his seat to conduct an unorthodox procedure when his co-pilot apparently lost control of the jet, two people familiar with the investigation said.

According to Reuters, the maintenance problems on the flight augmentation computer (FAC) and the way the pilots reacted to them are key are at the heart of the investigation.

People familiar with the matter said it was the Indonesian captain Iriyanto who tried to reset the computer and pulled a circuit-breaker to cut its power, rather than his less experienced French co-pilot Remy Plesel, who was flying the plane.

The captain had reportedly flown the same plane with the faulty device days earlier, but this has not been confirmed.

"You can reset the FAC, but to cut all power to it is very unusual," said one A320 pilot, who did not want to be named.

"You don't pull the circuit breaker unless it is an absolute emergency. I don't know if there was one in this case, but it is very unusual."

Experts told Bloomberg News that the loss of the FAC would not directly upset the aircraft but would remove flight envelope protection, which prevents a pilot from taking a plane beyond its safety limits, leaving the crew to fly the plane manually.